David Kelly’s father Patrick was a private in the Irish army and was murdered by the IRA in December 1983.
He was shot dead without warning by an IRA murder-kidnap gang in Derrada Wood, Ballinamore, Co Leitrim at the age of 36. He left behind a wife and four sons.
Mr Kelly said he confronted Sinn Fein’s Martin McGuinness “face-to-face” during his presidential election campaign in his home town in 2011 and asked for help in finding his father’s killers.
“He told me it was time to move on. He said that to my face,” Mr Kelly told those gathered at the event, prompting a collective gasp of horror.
The Irish Times quoted Mr McGuinness as having told him: “This is in the past, you are heartbroken on account of it and my sympathy is 100 per cent with you and your family.”
Mr Kelly added that there must be “some form” of truth and justice before there can be reconciliation.